In next generation multimedia mobile communication systems, which have been actively studied in recent years, there is a demand for a system capable of processing and transmitting a variety of information (e.g., video and radio data) in addition to the early-stage voice service. Wireless communication systems are widely spread all over the world to provide various types of communication services such as voice or data. The wireless communication system is designed for the purpose of providing reliable communication to a plurality of users irrespective of their locations and mobility. However, a wireless channel has an abnormal characteristic such as path loss, noise, fading due to multipath, an inter-symbol interference (ISI), the Doppler effect due to mobility of a user equipment, etc. Therefore, various techniques have been developed to overcome the abnormal characteristic of the wireless channel and to increase reliability of wireless communication.
Multiple input multiple output (MIMO) is a technique for supporting reliable high-speed data services. The MIMO technique improves data transmission/reception efficiency by using multiple transmit antennas and multiple receive antennas. Examples of the MIMO technique include spatial multiplexing, transmit diversity, beamforming, etc. A MIMO channel matrix depending on the number of receive antennas and the number of transmit antennas can be decomposed into a plurality of independent channels. Each independent channel is referred to as a spatial layer or a stream. The number of streams is referred to as a rank.
As a mobile communication system of a next generation (i.e., post-3rd generation), an international mobile telecommunication-advanced (IMT-A) system is standardized aiming at support of an Internet protocol (IP)-based seamless multimedia service in an international telecommunication union (ITU) by providing a high-speed transmission rate of 1 gigabits per second (Gbps) in downlink communication and 500 megabits per second (Mbps) in uplink communication. In a 3rd generation partnership project (3GPP), a 3GPP long term evolution-advanced (LTE-A) system is considered as a candidate technique for the IMT-A system. The LTE-A system is evolved to increase a completion level of the LTE system, and is expected to maintain backward compatibility with the LTE system. This is because the provisioning of compatibility between the LTE-A system and the LTE system is advantageous in terms of user convenience, and is also advantageous for a service provider since existing equipment can be reused.
Meanwhile, various uplink control information are transmitted on an uplink control channel. Examples of the uplink control information include a hybrid automatic repeat request (HARQ) acknowledgement (ACK)/not-acknowledgement (NACK), a channel quality indicator (CQI) indicating downlink channel quality, a scheduling request (SR) requesting resource allocation for uplink transmission, etc.
A plurality of UEs in a cell may simultaneously transmit uplink information to a base station (BS). The BS must be able to distinguish the uplink information simultaneously transmitted from the respective UEs. When the uplink information of the respective UEs are transmitted using different frequencies, the BS can distinguish the uplink information. A scheme of multiplexing a plurality of UEs by using mutually different frequencies is called frequency division multiplexing (FDM). The plurality of UEs in the cell may transmit the uplink information to the BS by using the same time-frequency resource. To distinguish the uplink information transmitted from the respective UEs by using the same time-frequency resource, the respective UEs may use orthogonal sequences in the transmission of the uplink information. Alternatively, the UEs may use low correlation sequences. As such, a scheme of multiplexing a plurality of UEs by using mutually different sequences is called code division multiplexing (CDM). Namely, uplink information of each UE may be multiplexed according to the CDM and/or FDM scheme and transmitted. In this respect, however, combining of the information transmission method based on the CDM scheme to a MIMO technique may cause a problem in that orthogonality is broken. With the orthogonality broken, it is more difficult for the BS to discriminate information of each UE than when the orthogonality is maintained. Thus, the reliability of wireless communication may deteriorate, and the overall system performance may be degraded.
Accordingly, there is a need for a method and an apparatus of effectively transmitting information by combining the MIMO technique and the CDM scheme and/or FDM scheme.